This invention relates generally to inkjet printhead structures, and more particularly, to active inkjet printhead structures for introducing ink into firing chambers from which ink is ejected onto print media.
An inkjet printhead includes multiple firing chambers for ejecting ink onto a print media to form characters, symbols and/or graphics. Typically, the ink is stored in a reservoir and passively loaded into respective firing chambers via an ink refill channel and respective ink feed channels. Capillary action moves the ink from the reservoir through the refill channel and ink feed channels into the respective firing chambers. Firing chambers typically occur as cavities in a barrier layer. Associated with each firing chamber is a firing resistor and a nozzle. The firing resistors are formed on a common substrate. The barrier layer is attached to the substrate. By activating a firing resistor, an expanding vapor bubble forms which forces ink from the firing chamber into the corresponding nozzle and out a nozzle orifice. A nozzle plate adjacent to the barrier layer defines the nozzle orifices. The geometry of the firing chamber, ink feed channel and nozzle defines how quickly a corresponding firing chamber is refilled after nozzle firing.
Typical passive loading of a nozzle chamber includes the rapid flow of ink into the chamber after firing. The ink flow action is characterized as a repeating flow and ebb process in which ink flows into the chamber, then back-flows slightly. Channel geometry defines passive damping qualities which limit the ink in-flow, while back-pressure and orifice diameter determine a steady-state chamber height. The flow and ebb cycle is passively damped until a steady state chamber level is maintained. The time to first achieve a steady state level is referred to as "refill time". The refill time limits the maximum repetition rate at which printhead nozzles can operate.
It is desired to achieve ejection of ink drops having known repeatable volume and shape. Firing a nozzle after a previous firing may result in either an "overshoot" or an "undershoot" condition. Overshoot is when the volume of ink in the firing chamber is above a steady state volume. Firing at such time causes a relatively larger droplet to be ejected. Undershoot is when the volume of ink in the firing chamber is below the steady state volume. Firing at such time causes a relatively smaller droplet to be ejected.
Current thermal inkjet printheads use a resistor multiplex pattern which allows the resistors to be fired at different times. Typically, the resistors are offset spatially to compensate for such timing. Typically, a vertical edge, or shelf, is formed along the ink refill channel. The ink feed channels are in fluid communication with the ink refill channel via the shelf. The respective resistors are staggered relative to the shelf, thereby creating different path lengths from the refill channel to the respective firing chambers. The differing path lengths result in different resistance to ink flow, and thus, vary the time it takes to refill each firing chamber. The different path lengths also vary the damping action at the firing chamber.
One challenge when implementing a multiplex pattern of adjacent resistors and firing chambers is to avoid cross-talk between neighboring firing chambers. Cross-talk, as used herein, refers to the condition during which fluid dynamics for one feed channel/firing chamber affects the fluid dynamics for another feed channel/firing chamber.